System for controlling light including a micromachined foucault shutter array and a method of manufacturing the same

ABSTRACT

An apparatus for controlling light includes a non-transparent surface for blocking incident light, an array of first lenses for focusing the incident light upon the non-transparent surface, an array of shutters corresponding to the array of first lenses and positioned on the non-transparent surface for controlling passage of the incident light through the non-transparent surface, and an array of second lenses corresponding to the array of shutters for collimating the incident light passing through the shutters. The shutters are separated from the first lenses by a distance equal to a focal distance of the first lenses such that the incident light is focused by the first lenses onto the shutters. As such, the shutters may be opened and closed to control the intensity of the incident light passing therethrough. Electrostatic comb drives corresponding to the array of shutters may be used for actuating the shutters, where the electrostatic comb drives each include two stationary stators that are separated by a distance at least as great as the largest shutter openings, and where the shutter includes two sliders that move relative to the stationary stators based on a magnitude of a voltage applied thereto. Alternatively, return springs may be used for biasing the shutters in an opened or closed position, and micromachine actuators for controlling actuation of the shutters. In either case, the shutters may be Foucault shutters, or other known shutters.

FIELD OF THE INVENTION

1. The present invention is directed to providing intensity modulationusing micromachine technology. In particular, intensity modulation isaccomplished by at least one microscopic shutter. The shutters arefabricated using lithographic micromachining techniques. The shuttersare incorporated into a system for controlling light, each shutter beinglocated at the focal point of a microlens array used to deliver lightto, and direct light from, a focal plane of the array.

BACKGROUND OF THE INVENTION

2. Conventionally, intensity modulation devices included liquid crystalsand tiltable mirrors. Such intensity modulators have disadvantages inthat light throughput efficiency and light power handling capacity areinsufficient and stray light noise is too high. In particular, theliquid crystal display suffers most greatly regarding the lightthroughput efficiency and light power handling capacity, while thetilting micromirrors suffer from stray light noise.

3. In addition, although conventional intensity modulation devices suchas liquid crystals are well-suited for large applications, they are notparticularly well-suited for regulating the intensity of light on amicroscopic scale. Rather, their large size renders them incapable ofefficiently operating to block incident light in applications requiringfine precision intensity regulation on a small scale.

4. In the absence of a device capable of regulating the intensity oflight on a microscopic scale, microscopic devices requiring such lightregulation have generally relied upon pulsed laser light. Similarly, todigitalize conventional devices that are optically driven withoutincreasing the size of those devices, pulsed laser light has been reliedupon. For instance, when printing devices are digitalized, laser diodeshave been conventionally used to regulate laser beams incident uponspecial paper where images are to be formed.

5. However, disadvantages frequently result when laser beams arerequired. For instance, when digitalizing printing devices as describedabove, an expensive type of special paper is required for printing andpower consumption of the printing device must be increased to generatelaser beams.

SUMMARY OF THE INVENTION

6. It is an object of the present invention to overcome all of thedisadvantages noted above. In particular, the present invention mayovercome these problems by using a true shutter. In other words, whenthe shutter in accordance with the present invention is open, 100% ofthe light is through put efficiently. When closed, all of the light isblocked, and not redirected as in the mirror systems.

7. Other and further objects, features and advantages of the presentinvention will be set forth in the description that follows, and in partwill become apparent from the detailed description, or may be learned bypractice of the invention.

8. To achieve these and other advantages and in accordance with thepurpose of the present invention, as embodied and broadly described, thepresent invention includes an apparatus for controlling light comprisinga non-transparent surface for blocking incident light, an array of firstlenses for focusing the incident light upon the non-transparent surface,an array of shutters corresponding to the array of first lenses andpositioned on the non-transparent surface for controlling passage of theincident light through the non-transparent surface, and an array ofsecond lenses corresponding to the array of shutters for collimating theincident light passing through the shutters. In this apparatus, theshutters are separated from the first lenses by a distance equal to afocal distance of the first lenses such that the incident light isfocused by the first lenses onto the shutters. As such, the shutters maybe opened and closed to control the intensity of the incident lightpassing therethrough.

9. The apparatus may further comprise electrostatic comb drivescorresponding to the array of shutters for actuating the shutters, wherethe electrostatic comb drives each include two stationary stators thatare separated by a distance at least as great as the largest shutteropenings, and the shutter include two sliders that move relative to thestationary stators based on a magnitude of a voltage applied thereto.Alternatively, the apparatus may include return springs for biasing theshutters in an opened or closed position, and micromachine actuators forcontrolling actuation of the shutters. In either case, the shutters maybe Foucault shutters, or other known shutters.

10. In addition, the present invention includes a method ofmanufacturing a micromachine Foucault shutter array that includesassembling an array of shutters on a non-transparent surface forcontrolling passage of incident light through the non-transparentsurface, assembling an array of first lenses corresponding to the arrayof shutters for focusing incident light upon the non-transparentsurface, positioning the array of first lenses relative to thenon-transparent surface such that the incident light is focused upon theshutters by the first lenses, and assembling an array of second lensescorresponding to the array of shutters for collimating the incidentlight passing through the shutters. Electrostatic comb drives and/ormicromachine actuators may be installed to control actuation of theshutters, thereby opening and closing the shutters to control theintensity of incident light passing therethrough. Electrostatic combdrives include two stationary stators that are separated by a distanceat least as great as the largest possible opening in the shutters, wherethe shutters each include two sliders that move relative to thestationary stators based on a magnitude of a relative voltage appliedthereto. Return springs may also be installed for biasing the shutter inan opened or closed position.

11. Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in this art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

12. The present invention will become more fully understood from thedetailed description given hereinbelow in the accompanying drawingswhich are given by way of illustration only and thus are not limited tothe present invention:

13.FIG. 1 shows a lens array in conjunction with the Foucault shutterarray of the present invention;

14.FIG. 2 shows a single element of the array shown in FIG. 1 in moredetail;

15.FIG. 3A shows in a single pixel detail the electrostatic drivemechanism of the single Foucault shutter in the closed position;

16.FIG. 3B shows electrostatic drive mechanism of a single Foucaultshutter in an open position;

17.FIGS. 3C and 3D show exemplary pictures of an interrelationshipbetween stators 24 and slides 26, each having comb parts that can bemoved together or apart depending upon whether the shutter is opened orclosed;

18.FIG. 4 shows a flowchart corresponding to an exemplary method ofmanufacturing a micromachine Foucault shutter array according to thepresent invention; and

19.FIGS. 5A-5C illustrate steps in an exemplary process formanufacturing comb parts of a shutter according to the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

20. As shown in FIG. 1, the microlens array 10 in accordance with thepresent invention is used to cause incident light to pass into and outof focus. In particular, a first refractive lenslet array 10 causeslight incident thereon to be focussed onto an opaque screen 12 locatedat a focal plane of the lenslet array 10. The opaque screen 12 has anarray of Foucault shutters 14, each corresponding to a refractive ordiffractive lens of the lenslet array 10. Thus, light on the focal planemay only pass through an opening provided by the Foucault shutter.Depending upon the state of the corresponding Foucault shutter, thelight diverges from the focal plane until it intercepts a secondrefractive or diffractive microlens array 16, which collimates thislight to form a transmitted beam.

21. As can be seen in FIG. 1, the amount of light delivered to thesecond lenslet array 16 is controlled by the state (open/closed) of acorresponding Foucault shutter in the array 14. As shown therein, aFoucault shutter 14 a is sufficiently closed such that no light passesfrom the lens 10 a to the lens 16 a. Foucault shutters 14 b, 14 c arepartially open such that some light passes from lenses 10 b, 10 c tolenses 16 b, 16 c, respectively. A Foucault shutter 14 d is sufficientlyopen that 100% throughput is achieved from lens 10 d to lens 16 d. Thedifferent degrees of light throughput result in the desired intensitymodulation. Another method of performing intensity modulation is to varythe time that the shutter is open, with short shutter open timecorresponding to low light level and long shutter open timecorresponding to bright light level.

22.FIG. 2 is a more detailed view of a single channel of theconfiguration shown in FIG. 1. The Foucault shutter can be either biasedin a closed position by a return spring 22 or biased in an open positionby a return spring. The state of the Foucault shutter is controlled by amicromachine actuator 20.

23. In employing a Foucault shutter array in accordance with the presentinvention, it is advantageous to use shutters which do not requiremechanical interaction for control thereof. A suitable shutter, employedin different application than providing intensity modulation, is a knownelectrostatic drive lateral comb interdigitated drive. With lateral combdrives, the activation is parallel with the substrate. The forcegenerated by the lateral comb drives is independent of the relativeposition of the two electrode plates, while the plates overlap. Lateralcomb drives can produce large deflections necessary for use in, forexample, a gyroscopic application. For example, displacements of 20microns have been achieved.

24. In the preferred embodiment of the present invention, a lateral combdrive is adapted for use as the actuation mechanism for the Foucaultshutter array 14. A shutter incorporating lateral comb drives for usewith the present invention is shown in FIGS. 3A and 3B. The shutterincludes two stationary stators 24 and two sliders 26, the two slides 26remaining free to move relative to the stationary stators 24. Thesliders 26 form the Foucault shutter, while the stators 24 control thespacing therebetween. As shown in FIGS. 3C and 3D, the stators 24 andslides 26 each have comb parts, the proximity of the comb parts of theshutter and the comb parts of the actuator being based on whether theshutter is opened or closed.

25. When no voltage is applied, the ribbon springs 28 hold the twosliders 26 together in a closed position, as shown in FIG. 3A. When avoltage is applied between the sliders 26 and the stators 24, the twosliders 26 move toward their respective stators, as can be seen in FIG.3B. As the sliders 26 move apart, a small aperture 29 is revealed, asshown in FIG. 3B. This aperture 29 serves as the shutter opening and canbe controlled by varying the magnitude of the applied voltage. The sizeof this aperture will determine the amount of the light beam passingtherethrough.

26. Therefore, intensity modulation of light may be effectively achievedon a microscopic scale using a true shutter. Electrical forces of thecomb drive provide the movement required for the requisite opening ofthe shutter. When the voltage is removed, the shutter will return to theclosed position. Alternatively, when the voltage is applied, the shuttercould be closed, and when the voltage is removed, the shutter could beopened by the springs.

27. By using the shutter to achieve intensity modulation of light on amicroscopic scale, the present invention may either regulate thetransmission or reflection of light, or both. For instance, if thesurface of the shutter is neither transparent nor reflective, thepresent invention modulates only the transmission of light incidentthereupon.

28. However, in an alternative embodiment where the shutter surface isreflective, the present invention may be utilized to modulate either thetransmission or reflection of light incident thereupon. Morespecifically, in this alternative embodiment, although light istransmitted when the shutter is opened, light is reflected from thesurface of the shutter when the shutter is closed. As such, both thereflected and transmitted light are modulated based on the actuation ofthe shutter.

29. Furthermore, an alternative embodiment includes a single stator anda single slider, the single slider moving relative to the single statorsimilar to the operation described above with respect to a pair ofsliders.

30. An exemplary application of the above-described shutter involvesdigitalized printing devices. With these shutters, regular light may bemodulated to achieve digital signals appropriate for digital imaging.Thus, printing devices may be fitted with these devices to achievedigitalization, without requiring pulsed laser diodes, laser light orthe special paper conventionally required of digital printing devices.

31.FIG. 4 shows a flowchart corresponding to an exemplary method ofmanufacturing a micromachine Foucault shutter array according to thepresent invention. In step 41, an array of shutters 14 is assembled on anon-transparent surface 12 for controlling passage of incident lightthrough the non-transparent surface 12. In steps 42 and 43, actuators 20are installed for actuating the shutters 14 to control incident lightpassing therethrough, and springs 22 or other biasing elements areinstalled to bias the shutter 14 in an opened or closed position.Exemplary actuators 20 may include micromachine actuators (see FIG. 2)or electrostatic comb drives (see FIGS. 3A-3B). Electrostatic combdrives include two stationary stators 24 that are separated by adistance at least as a large as the possible opening in the shutters 14,where the shutters 14 include two sliders 26 that move relative to thestationary stators 24 based on a magnitude of a voltage applied thereto.For instance, as shown in FIGS. 3C and 3D, the stators 24 and slides 26each have comb parts, the proximity of the comb parts of the shutter andthe comb parts of the actuator being based on whether the shutter isopened or closed. When electrostatic comb drives are used, springs 22are not necessary for biasing the shutters 14, rather a voltage or lackthereof can be used to bias the shutters 14 into an opened or closedposition.

32. In step 44, an array of first lenses 10 corresponding to the arrayof shutters 14 is assembled for focusing incident light upon thenon-transparent surface 12. In step 45, the array of first lenses 10 ispositioned relative to the non-transparent surface 12 such that theincident light is focused upon the shutters 14 by the first lenses 10.In step 46, an array of second lenses 16 corresponding to the array ofshutters 14 is assembled for collimating the incident light passingthrough the shutters 14.

33. To fabricate the shutters within the array assembled in step 41 ofFIG. 4, several processes may be used. One process used to fabricatethese shutters is to use reactive ion etching (RIE). In this method, aplasma etching gas is used to etch a first material rapidly whileetching a second material very slowly, the second material being knownas a mask material. As such, the structure of the shutter can beconstructed using known photolithographic methods like the methods usedfor making microelectronic circuits. In fact, using this method, severalstructures can be made on a single substrate in a manner similar to themethod of making several microcircuits on a single substrate.

34. More specifically, a method of fabricating a single shutter withinthe array assembled in step 41 of FIG. 4 is described hereinafter withrespect to FIGS. 5A-5C. As shown in FIG. 3B, FIGS. 5A-5C represent across-sectional view of a portion of the comb part on slide 26 of theshutter. As such, for reference purposes, the resulting comb part 54shown in FIG. 5C is moved into the page or out from the page by anactuator in order to open and close the shutter. Although not shown inFIGS. 5A-5C, the simultaneous fabrication of the body of the slider 26upon which the comb part 54 is engaged will also be describedhereinafter.

35. In the first step of the fabrication process shown by FIG. 5A, aCMOS microcircuit is fabricated with at least one mask layer 50positioned within silicon dioxide layer 51 above silicon substrate 52.The CMOS microcircuit may be fabricated using standard availableprocesses such as those commonly used by Intel, HP, Orbit Semiconductor,etc.

36. The second step involves lithographically etching the silicondioxide layer 51, e.g., using RIE with CHF₃ and O₂ gases, therebyexposing a substrate surface region 55 as shown by FIG. 5B. In a regionbehind that shown in FIG. 5B, the etching of the silicon dioxide layer51 exposes the body of slider 26 to which the illustrated layer isattached, and under which a substrate aperture is formed.

37. In the third step, illustrated by FIG. 5C, the structure 54 isisolated from the substrate 52 by etching the substrate surface 55 to adepth of approximately 10 microns using either XeF₂ or SF₆, therebyundercutting the silicon dioxide SiO₂ upon which the mask layer(s) 50are narrowly formed. The resulting freestanding structure identified byreference numeral 54 represents the comb part of the comb drive. Thecomb part 54 of the comb drive moves in response to an electrostaticforce resulting from the application of voltage. The springs or otherbiasing elements installed in steps 45 and 46 may also be made of thesame SiO₂ metal as the above-described combs.

38. While there have been illustrated and described what are at presentconsidered to be preferred embodiments of the present invention, it willbe understood by those skilled in the art that various changes andmodifications may be made, and equivalents may be substituted forelements thereof without departing from the true scope of the presentinvention. In addition, many modifications may be made to adapt aparticular situation or material to the teaching of the presentinvention without departing from the central scope thereof. Therefor, itis intended that the present invention not be limited to the particularembodiment disclosed as the best mode contemplated for carrying out thepresent invention, but that the present invention includes allembodiments falling within the scope of the appended claims.

39. The foregoing description and the drawings are regarded as includinga variety of individually inventive concepts, some of which may liepartially or wholly outside the scope of some or all of the followingclaims. The fact that the applicant has chosen at the time of filing ofthe present application to restrict the claimed scope of protection inaccordance with the following claims is not to be taken as a disclaimerof alternative inventive concepts that are included in the contents ofthe application and could be defined by claims differing in scope fromthe following claims, which different claims may be adopted subsequentlyduring prosecution, for example, for the purposes of a continuation ordivisional application.

What is claimed is:
 1. An apparatus for controlling light, comprising: amicromachined shutter positioned over an aperture in a non-transparentsubstrate for regulating light passing through the aperture of thenon-transparent substrate; and a micromachined comb drive actuator foropening and closing the micromachined shutter.
 2. The apparatus recitedby claim 1 , wherein the micromachined shutter is fabricated usinglithographic techniques.
 3. The apparatus recited by claim 1 , whereinthe micromachined shutter includes at least one slider that is movedrelative to a stationary stator based on the micromachined comb driveactuator to modulate light passing therethrough.
 4. The apparatusrecited by claim 1 , wherein the shutter and the comb drive actuatoreach include comb parts, the proximity of the comb parts of the shutterand the comb parts of the actuator being based on whether the shutter isopened or closed.
 5. The apparatus recited by claim 1 , wherein: themicromachined shutter is part of an array of micromachined shutterspositioned on the non-transparent substrate for regulating light passingthrough the non-transparent substrate; and the micromachined comb driveis part of an array of micromachined comb drive actuators, each drivingan associated one of the micromachined shutters within the array ofmicromachined shutters.
 6. The apparatus recited by claim 1 , whereinthe micromachined shutter is adapted for use in a printing device.
 7. Amethod of manufacturing a shutter, comprising: providing a substratewith an aperture defined therein and at least two layers depositedthereon; and lithographically etching a portion of a first layer and aportion of the substrate to isolate a freestanding portion of the secondlayer with respect to the substrate, the freestanding portion of thesecond layer forming a portion of the shutter which is moved withrespect to the substrate to control incident light passing through theaperature of the substrate.
 8. The method recited by claim 7 , whereinlithographically etching the portion of one layer and the substratecomprises: etching a portion of the first layer to expose at least twosurface portions of the substrate; and etching a portion of thesubstrate to isolate a freestanding portion of the second layer withrespect to the substrate.
 9. The method recited by claim 7 , wherein thefreestanding portion of the second substrate is a comb part that ismoved relative to a comb part of the substrate to actuate the shutter.10. The method recited by claim 7 , further comprising: lithographicallyetching a different region of the first layer and the substrate toisolate another freestanding portion of the second layer used to biasthe shutter position.
 11. A shutter formed by the process of: providinga substrate with an aperture defined therein and at least two layersdeposited thereon; and lithographically etching a portion of a firstlayer and a portion of the substrate to isolate a freestanding portionof the second layer with respect to the substrate, the freestandingportion of the second layer forming a portion of the shutter which ismoved with respect to the substrate to control incident light passingthrough the aperature of the substrate.
 12. The shutter recited by claim11 , wherein the process of lithographically etching the portion of onelayer and the substrate comprises: etching a portion of the first layerto expose at least two surface portions of the substrate; and etching aportion of the substrate to isolate a freestanding portion of the secondlayer with respect to the substrate.
 13. The shutter recited by claim 11, wherein the freestanding portion of the second substrate is a combpart that is moved relative to a comb part of the substrate to actuatethe shutter.
 14. The shutter recited by claim 11 , wherein the processfurther comprises: lithographically etching a different region of thefirst layer and the substrate to isolate another freestanding portion ofthe second layer used to bias the shutter position.
 15. A method ofmanufacturing an apparatus for controlling light, comprising: assemblingan array of shutters on a non-transparent surface for controllingpassage of incident light through a non-transparent surface; assemblingan array of first lenses corresponding to the array of shutters forfocussing incident light upon the non-transparent surface; andpositioning the array of first lenses relative to the non-transparentsurface such that the incident light is focussed upon the shutters bythe first lenses.
 16. The method recited by claim 15 , furthercomprising: assembling an array of second lenses corresponding to thearray of shutters for collimating the incident light passing through theshutters.
 17. The method recited by claim 15 , wherein the shutters arecapable of being opened and closed to control the intensity of theincident light passing therethrough.
 18. The method recited by claim 17, further comprising: installing electrostatic comb drives correspondingto the array of shutters for actuating the shutters.
 19. The methodrecited by claim 18 , wherein: the electrostatic comb drives eachcomprise two stationary stators that are separated by a distance atleast as great as a largest possible opening in the shutters, and theshutters each comprise two sliders that move relative to the stationarystators based on a magnitude of a voltage applied thereto.
 20. Themethod recited by claim 17 , further comprising: installing returnsprings for biasing the shutters within the array of shutters in an openor closed position; and installing micromachine actuators forcontrolling actuation of the shutters within the array of shutters. 21.The method of manufacturing recited by claim 15 , wherein the array ofshutters is an array of Foucault shutters, a method of manufacturing theFoucault shutters including: etching a microcircuit to expose a masklayer and at least two surface portions of a substrate upon which themicrocircuit is positioned; and undercutting a portion of themicrocircuit located between the two exposed surfaces of the substrateby etching the substrate at the exposed portions and under the undercutportion to produce a movable shutter element.
 22. An apparatus forcontrolling light comprising: a non-transparent surface for blockingincident light; an array of first lenses for focussing the incidentlight upon the non-transparent surface; and an array of shutterscorresponding to the array of first lenses and positioned on thenon-transparent surface for controlling passage of the incident lightthrough the non-transparent surface, wherein the shutters are separatedfrom the first lenses by a distance equal to a focal distance of thefirst lenses such that the incident light is focussed by the firstlenses onto the shutters.
 23. The apparatus recited by claim 22 ,further comprising: an array of second lenses corresponding to the arrayof shutters for collimating the incident light passing through theshutters.
 24. The apparatus recited by claim 22 , wherein the shuttersare opened and closed to control the intensity of the incident lightpassing therethrough.
 25. The apparatus recited by claim 24 , furthercomprising: electrostatic comb drives corresponding to the array ofshutters for actuating the shutters.
 26. The apparatus recited by claim25 , wherein: the electrostatic comb drives each comprise two stationarystators that are separated by a distance at least as great as a largestshutter opening, and the shutters each comprise two sliders that moverelative to the stationary stators based on a magnitude of a voltageapplied thereto.
 27. The apparatus recited by claim 24 , furthercomprising: return springs for biasing the shutters within the array ofshutters in an open or closed position; and micromachine actuators forcontrolling actuation of the shutters within the array of shutters. 28.The apparatus recited by claim 24 , wherein shutters within the array ofshutters are Foucault shutters.
 29. The apparatus recited by claim 21 ,wherein the apparatus is adapted for use in a printing device.